Inventory no. 53820 - Former Display Label
German FOLDING SQUARE and PROTRACTOR
18th century
Brass. Unsigned and undated.
The outer edges of the two arms are bevelled. On
the front of the arms is a trigonometric scale of 180°
divided by transversals to fifteen minutes of arc,
inscribed, 'Grad Linigte Transporteur muss bis 60.
eröffnet und ein Bogen gerissen Werden". With a
pair of dividers, this scale serves as a protractor.
An arc is drawn having as radius the distance from 0°
to 60° on the scale, and the required angle is
measured off the scale with dividers and transferred
to the arc. The two points where the dividers cut
the arc will subtend the required angle at the centre
of the arc.
On the back are a diagonal scale and three linear
scales in which four divisions equal 93, 101 and
108 mm. respectively.
[57-84/264] Billmeir Collection